SEARCH FOR COINCIDENT NEUTRINOS FROM LUMINOUS ASTROPHYSICAL TRANSIENTS WITH THE ICECUBE NEUTRINO DETECTOR

Abstract

The origin of high energy cosmic rays has been a long standing mystery in the field of particle astrophysics. Cosmic rays are energetic charged particles that constantly bombard Earth's atmosphere. Since cosmic rays are electrically charged, they are deflected through interstellar magnetic fields on their way to Earth, which makes the origins of these objects difficult to trace. Neutrinos are created in the same interactions as cosmic rays, but because they are electrically neutral, neutrinos do point back to their sources. Finding neutrino emission from an astrophysical object would provide confirmation that the astrophysical source produces cosmic rays. IceCube is a cubic-kilometer neutrino detector located at the South Pole. IceCube's completion marked the beginning of a new age of multi-messenger astronomy where multiple messengers, such as photons and neutrinos (and slightly later gravitational waves), could be used to examine a single astrophysical source. This thesis examines two potential astrophysical sources of neutrino emission: GRB 221009A and Luminous Fast Blue Optical Transients (LFBOTs). Gamma-ray bursts (GRBs) are extremely luminous, short bursts of gamma-rays caused by a kilonova or mergers of compact objects such as black holes or neutron stars. GRBs were once thought to be a main source of neutrino emission, but IceCube searches have found no significant excess of neutrino emission from over 2,000 GRBs. GRB 221009A was the brightest gamma-ray burst ever detected. This event captivated the astrophysical community and sparked several multi-messenger follow-ups, including a coordinated analysis with the IceCube neutrino detector. The IceCube analysis used several datasets that span IceCube's energy range and utilized several time windows to search for neutrino emission during the precursor, prompt emission, and a potential afterglow. There was no significant neutrino emission found in any of the time windows searched across the entire energy range. World-leading upper limits were placed on the neutrino emission from gamma-ray bursts due to the exceptional nature of this source that constrained several GRB models. This thesis also discusses the first dedicated search for neutrinos from LFBOTs, a new source class based on AT 2018cow. AT 2018cow was also an extremely luminous astrophysical object, but displayed multiple unusual properties. The main emission from this object was blue optical light, but it also emitted in X-ray and radio. Notably the source was lacking supernova emission lines and gamma-ray emission. This unusual object sparked interest across the astrophysical community and resulted in a realtime follow-up from IceCube. This follow-up found two neutrinos in spatial coincidence with the source, within days prior to optical emission. While not a significant result, this provided tantalizing evidence that this type of object could be a source of neutrino emission, if more similar objects were discovered. A catalog search and a stacked search for neutrino emission were performed using 10 LFBOTs, searching a minus two day and plus twelve day time window around the first discovery of optical emission. No significant neutrino emission was found in either analysis, but upper limits were set that constrained the Choked Jet model. Ultimately, a more complete catalog is needed to determine if LFBOTs are a source of astrophysical neutrinos. Next generation optical telescopes, such as the Vera Rubin Observatory, will discover hundreds of LFBOTs, and next generation neutrino telescopes, such as IceCube Gen-2, will have improved sensitivity to neutrino emission.